Superconductors for high currents have been technically established for some considerable time. Superconductors conduct a direct current without loss. However, as soon as the superconductor current fluctuates in time or the conductor is situated in a fluctuating magnetic field, losses occur which raise the operating temperature of the conductor and in so doing lower the conductivity. Furthermore, the losses have to be removed at low temperatures. Normal operating temperatures are 4.2 to 5.0 K, and permissible temperature rises usually not more than 0.3 degrees.
It is known that the losses in the superconducting material (e.g., NbTi, Nb.sub.3 Sn) can be reduced by dividing the superconductor into a number of filaments. The superconductor filaments are embedded in a matrix which in the case of NbTi superconductors is usually of copper or aluminum, and in the case of Nb.sub.3 Sn superconductors is of a bronze with or without a copper lining. Along the filaments there flow eddy currents which at the end of the conductor cross through the matrix into other filaments and flow back in the latter. Owing to the very electrical resistance in this loop, the eddy currents persist for a long time and give rise to high losses. It is known that these losses can be reduced by twisting the conductor comprising matrix and filaments or by increasing the specific resistance of the matrix between the filaments. For technical reasons (great unit length, economy) superconductors are composed of stranded single conductors. Here, too, as in a single conductor, coupling losses occur which can be reduced by stranding the cables with a short lay. The further the filaments in a single conductor or in cables are away from each other, the higher are the losses and the tighter is the lay required. These tendencies are contradictory because thick cables cannot be twisted as sharply as thin ones.
Methods of insulating the component elements are superconductor cables from each other, or of separating them spatially with high-resistance basic supporting materials, are already known. A solution is described and illustrated in "Proc. V. Int. Conf. on Magnet, Techn.", Rome 1975. The individual wires are insulated from each other by oxide layers. This arrangement does not ensure good insulation, however, because the oxide layers are brittle and so short circuits can occur. In DT-OS No. 22 40 282 a superconductor is described which consists of a number of superconducting wires so arranged as to form a braid, and has an outer sheath which surrounds the braid, the braid inside the sheath being surrounded by a layer of plastic. Each conductor is thus completely insulated and therefore each individual conductor must remain fully operational. Cooling of the conductor is severely impeded. A strip-shaped conductor with several single conductors is described in DT-AS No. 22 56 594. Here the single conductors each contain several superconductors, they are attached to a flat side of an armour strip side by side and are arranged at a prescribed distance from each other. This arrangement provides a high-resistance connection between the individual conductors, but fixing a large number of single conductors to the base and joining them to the end conductor (and here again twisting is necessary) is uneconomical.